diff --git a/src/core/enumerable.js b/src/core/enumerable.js
index 2fd38b3..0bac423 100644
--- a/src/core/enumerable.js
+++ b/src/core/enumerable.js
@@ -1608,11 +1608,11 @@
         };
 
         OrderedEnumerablePrototype.thenBy = function (keySelector, comparer) {
-            return this.createOrderedEnumerable(keySelector, null, false);
+            return this.createOrderedEnumerable(keySelector, comparer, false);
         };
 
         OrderedEnumerablePrototype.thenByDescending = function (keySelector, comparer) {
-            return this.createOrderedEnumerable(keySelector, comparer, false);
+            return this.createOrderedEnumerable(keySelector, comparer, true);
         };
 
         return OrderedEnumerable;